T his article presents the background on the development of solid-state lighting technology, which is gaining popularity as a light source application. This review focuses on the main characteristics of solid-state lighting devices as well as their supply requirements and the effect of temperature on light-emitting diode (LED) performance. LED drivers are designed to achieve the best operation conditions without degrading the longer lifetime that this technology achieves in comparison to other popular light sources. Offline LED drivers include active power factor correction while current control with low ripple is required to supply the LED units or string arrangements. Methods to achieve balanced current sharing on paralleled LED strings and some of the latest contributions on LED drivers are also explained.

The proliferation of nonlinear loads and the increasing penetration of distributed energy resources in medium-voltage (MV) and low-voltage (LV) distribution grids make it more difficult to maintain the power quality levels in residential electrical grids, especially in the case of weak grids. Most household appliances contain a conventional power factor corrector (PFC) rectifier, which maximizes the load power factor (PF) but does not contribute to the regulation of the voltage total harmonic distortion (THD _V ) in residential electrical grids. This paper proposes a modification for PFC controllers by adapting the operation mode depending on the measured THD _V . As a result, the PFCs operate either in a low current total harmonic distortion (THD _I ) mode or in the conventional resistor emulator mode and contribute to the regulation of the THD _V and the PF at the distribution feeders. To prove the concept, the modification is applied to a current sensorless nonlinear controller applied to a single-phase boost rectifier. Experimental results show its performance in a PFC front-end stage operating in the continuous conduction mode connected to the grid with different THD _V .

A new digital control technique for power factor (PF) correction is presented. The main novelty of the method is that there is no current sensor. Instead, the input current is digitally rebuilt, using the estimated input current in the current loop. The circuit measures the input and output voltage by means of low cost ad hoc analog-to-digital converters (ADCs). Taking advantage of the slow dynamic behavior of these voltages, almost completely digital ADCs have been designed, leaving only a comparator and an RC filter in the analog part. Avoiding measuring current can provide a significant advantage compared to analog controllers and this also helps to reduce the total cost. The ultimate objective is to obtain a low-cost digital controller that can be easily integrated as an intellectual property (IP) block into a field-programmable gate array, or an application-specific integrated circuit. The experimental results show a reasonably high PF, despite not measuring the input current, and therefore the feasibility of the method.

Continuous conduction mode power factor correction (PFC) without input current measurement is a step forward with respect to previously proposed PFC digital controllers. Inductor volt-second (vs_L) measurement in each switching period enables digital estimation of the input current; however, an accurate compensation of the small errors in the measured vs_L is required for the estimation to match the actual current. Otherwise, they are accumulated every switching period over the half-line cycle, leading to an appreciable current distortion. A vs_L estimation method is proposed, measuring the input (v_g) and output voltage (v_o). Discontinuous conduction mode (DCM) occurs near input line zero crossings and is detected by measuring the drain-to-source MOSFET voltage v_ds. Parasitic elements cause a small difference between the estimated voltage across the inductor based on input and output voltage measurements and the actual one, which must be taken into account to estimate the input current in the proposed sensorless PFC digital controller. This paper analyzes the current estimation error caused by errors in the ON-time estimation, voltage measurements, and the parasitic elements. A new digital feedback control with high resolution is also proposed. It cancels the difference between DCM operation time of the real input current, (T_DCM^g) and the estimated DCM time (T_DCM^reb). Therefore, the current estimation is calibrated using digital signals during operation in DCM. A fast feedforward coarse time error compensation is carried out with the measured delay of the drive signal, and a fine compensation is achieved with a feedback loop that matches the estimated and real DCM time. The digital controller can be used in universal applications due to the ability of the DCM time feedback loop to autotune based on the operation conditions (power level, input voltage, output voltage...), which improves the operation range in comparison with previous solutions. Experimental results are shown for a 1-kW boost PFC converter over a wide power and voltage range.

The LC/sub s/C/sub p/ resonant converter finds a new application in an electrical discharge machining (EDM) power supply, which is designed for the purpose of developing small size EDM systems. The switching frequency is tuned to the natural resonant frequency where the converter tends to act as a current source. In this way, three effects are achieved: 1) the necessary over-voltage is generated, first to ionize the dielectric and then to establish the electric discharge, 2) a constant current is supplied during the machining of the workpiece, providing the circuit with inherent protection under short circuit conditions, and 3) overall stability is guaranteed despite the equivalent negative resistance of the dielectric breakdown. The proposed control achieves an optimum and stable operation using tap water as dielectric fluid preventing the generation of undesired impulses and keeping the distance between the electrode and the workpiece within the optimum stable range. The EDM power supply has been validated to perform operations in a nuclear power plant application.

Current-mode control in digitally controlled switched-mode power supplies typically requires analog-to-digital (A/D) conversion of at least two signals, voltage, and current. The complexity of voltage A/D converters can be reduced using window A/D techniques. In conventional current A/D conversion, however, relatively high resolution is required over a wide range of signals, which results in increased complexity, power consumption, and cost of the controller. This paper proposes a very simple feedback sensor capable of high-resolution average inductor current sensing using two analog comparators and an analog low-pass filter. The approach requires very few external components and employs minimal digital hardware resources. A dynamic model and performance of the average inductor current sensor are experimentally verified on a 12-V input, 19-V output, 50-W boost converter prototype. The applicability of the proposed sensor is demonstrated in a digitally controlled 400-W, 400-V output Boost power factor preregulator.